Rough Idle - P1336 - High misfire on several cylinders

Hi

I am going round in circles trying to find the root cause of a fault on My Mums C3…trawled the internet and asked a couple of garages / mechanics but no one can tell me exactly what’s wrong with it or give us a cost to fix it…hope someone can help

Car started making a ‘puffing’ noise from the exhaust…thought it was the exhaust blowing , so took it to our local garage, they couldn’t find anything wrong with the exhaust and couldn’t work out what was causing it…a couple of days later the engine light came on and the car stated rough idling, periodically going into what I think is limp mode (Engine light flashes)…

P1336
Raw code: 1336
ECU: 10
Status: Confirmed
OBDII: Crank / Cam Sensor Range / Performance
Citroen: Crank/Cam sensor range/performance  S2000PM1/2 - High misfire on several cylinders  ME7.4.5. Combustion misfiring on unspecified cylinders.

Changed the Coil Pack & Plugs…No Change
Ran for 2 Weeks with Redex Fuel Additive
Compression Test = C1-140 / C2-145 / C3-135 / C4-150

Garage think its a stuck / burnt valve - asking £600+ to take head off and check / reseat…but no guarantee that’s the actual fault!

Help…Please!

goingquietlymad wrote: ↑Sat Mar 06, 2021 8:53 pm Garage think its a stuck / burnt valve

Hi

This is very possible, and you took it to a garage that could hear the engine (something we can't do).

you have done tests and tried some remedies and it wasn't the solution.

Why not go with their best suggestion?

Seems like the best way forward.

You could even remove the head - yourself? and if its damaged and don't want to pay for a recon head and its fitting then get it scrapped.
If it is not the valve then a new head gasket never did any harm with these engines.

The code P1336 is probably "misfiring on unspecified cylinders". It just means the crank angle sensor has detected that one or more of the cylinders did not perform full combustion when the engine ECU expected it to. Not very helpful but if it was the coil pack the engine ECU would have picked it up. But you know that as it was not the coil pack.

Look up burnt/stuck valves on Youtube.

The primary symptom is air being sucked back into the exhaust pipe.

Put a piece of paper over the exhaust pipe and see if it tries to get sucked back onto the pipe. If the piece of paper only blows off the pipe it's not the valve.

Pull the spark plugs out. Inspect the electrode area:

If one of the plugs has thin white deposits on it that's a burnt/sticking/fouled valve. This is signs of a lean mixture, as the cylinder is sucking in air from the exhaust valve and the inlet valve.

If you have some black plugs and some good plugs. It might be a (or more than 1) fuel injector. The good plugs will be the cylinders with black/sooty deposits on them. The engine ECU will be over compensating by putting too much fuel into the good injectors. Blocked fuel injector(s) can make a chuffing sound too.
If you go to this page and scroll down about 1/2 way you will see the troubles I had with fuel injectors;
the-citroen-c3-club-area-whats-great-ab ... t3521.html

Hi Ozvtr

Took the car for a blast down the motorway, not too far, not too fast...runs great (at speed)

Rough Idle is much the same, but re-checked the error codes...

P0352 - OBDII: Ignition coil B, primary/secondary - circuit malfunction
P0351 - OBDII: Ignition coil A, primary/secondary - circuit malfunction
P0108 - OBDII: Manifold absolute pressure (MAP) sensor/barometric pressure (BARO) sensor - high input
P0113 - OBDII: Intake air temperature (IAT) sensor - high input
P0302 - OBDII: Cylinder 2 - misfire detected
P1338 - OBDII: #8 MISFIRE CIRCUIT - OPEN - Citroen: ME7.4.5. Cylinder No.2 misfires.

Checked your points:

Paper over the exhaust - flaps about a lot but gets sucked in if you hold it close
All plugs are dry and look ok....however the top / face and rim of the electrode on plug 2 is white / grey...

Car is going to an engine specialist this week for a quote for head off and valve reseat...

Thanks!

Not surprised it runs ok at high speed, the compression is not down that much. But I bet the acceleration is non-existent? Also if it was the coil pack you would get misfires at speed too. Coil pack misfires tend to be sharp and random. The misfires the ECU is logging will probably be at idle. Does the OBDII scanner tell you what the engine was doing at the time. Speed, RPM, engine temp?

The cylinders on the TU3 engine are labeled from the flywheel to the pulley (right to left as you look at the engine). Did you know that?

If you have got it right, then I think the garage got it wrong. Both you and the engine ECU report problems with the No2 cylinder. According to the report, the No3 cylinder has low compression? If you got it wrong it doesn't matter as the No2 and No3 plugs fire at the same time anyway. Google; "wasted spark ignition". Gap on the spark plugs OK?

There are 4 wires coming from the MAP sensor to two different plugs on the engine ECU. So I would check the plug at the MAP sensor for firmness and perhaps ingress of moisture. Both the MAP sensor and the inlet manifold temp sensor are in the same device. FYI the MAP sensor sits on the front left hand (viewed from the front) end of the inlet plenum. Just to be sure, you could check the three big connectors on the engine ECU for moisture ingress too.

I don't know why the OBDII scanner keeps mentioning the BOSCH ECU (ME7.4.5). That's the 1.6 "sports" ECU used in the C2 and C4's. Is it just making a comment?

Any idea why these other faults didn't pop up before? Moved/touched/replaced something? Just forgot to mention them?

My apologies...should have read Compression Test = C1-150 / C2-135 / C3-145 / C4-140

Cylinder 2, Second in from the right / flywheel (looking at the front of the car)

Car going in on Thursday morning to an engine specialist to have a look, if they concur with the opinion that its a valve then they will remove the head, reseat 'all' valves, skim and refit...all for just shy of £700...

I am so far in with this car I am going for it!....if it all works out it could 'potentially' last my Mum until she gives up driving!


....Just curious though if it was a fault with the Injector would that not show a different / another fault code?....is it worth any final checks?


Thanks!...

goingquietlymad wrote: ↑Mon Mar 08, 2021 8:40 pm Car going in on Thursday morning to an engine specialist to have a look, if they concur with the opinion that its a valve then they will remove the head, reseat 'all' valves, skim and refit...all for just shy of £700...

How does that compare with a recon head? (+removal and fitting cost).

Until they have removed the head for inspection you won't know if it is fully serviceable anyway..

goingquietlymad wrote: ↑Mon Mar 08, 2021 8:40 pm
....Just curious though if it was a fault with the Injector would that not show a different / another fault code?

Depends on which code you are talking about. Different to which?

The engine ecu can detect shorted or open sensors (or electrical devices connected to it, like fuel injectors, electro-valves and the coil pack). It can read the sensor value and determine if its in the range it's expecting. It can look at when the crankshaft accelerates after a cylinder should fire. It can read the shape of the voltage waveform from the coil pack and determine if the plugs are firing correctly when they are supposed to.
What it can't do is detect physical anomalies in the engine. Like the fuel injectors being blocked or a burnt valve. All it can tell you is Cylinder X didn't combust properly when it should have but every thing else looks OK. Most of the time it cant even pin it down to a cylinder, it just says indeterminate misfire. Not much of a help but it does tell you that the ECU doesn't think there is anything wrong with the electrics...so what does that leave? Some sort of mechanical fault.

goingquietlymad wrote: ↑Mon Mar 08, 2021 8:40 pm ....is it worth any final checks?

Not that you can perform. If the mechanics are worth their salt they would put a bore-scope down the spark plug hole and look for damage to the piston crown that might show some other fault than a burnt valve. Like a crack in the top of the piston or something that might make moving on a waste of time.
They could test the injectors but is that a waste of time that you have to pay for? A good mechanic should be sure of their diagnosis and waste as little time as possible.
There are variables here, like, is there irreparable damage to the head and is the valve too damaged to re-seat and needs to be replaced?